1. Technical Field
Embodiments of the present invention relate generally to histidyl-tRNA synthetase polypeptides having improved characteristics, compositions comprising the HRS polypeptides, and related methods of using the HRS polypeptides or compositions to treat various inflammatory and autoimmune diseases, including methods of treating anti-Jo-1 antibody-related inflammatory and autoimmune diseases.
2. Description of the Related Art
Physiocrines are generally small, naturally-occurring, protein domains found in the aminoacyl-tRNA synthetases (AARSs) gene family of higher organisms, which are not required for the well-established role of aminoacyl-tRNA synthetases in protein synthesis. Until the Physiocrine paradigm was discovered, aminoacyl-tRNA synthetases, a family of about 20 enzymes, were known only for their ubiquitous expression in all living cells, and their essential role in the process of protein synthesis. More recent scientific findings however now suggest that aminoacyl-tRNA synthetases possess additional roles beyond protein synthesis and in fact have evolved in multicellular organisms to play important homeostatic roles in tissue physiology and disease.
Evidence for the existence of the non-canonical function of AARSs includes well defined sequence comparisons that establish that during the evolution from simple unicellular organisms to more complex life forms, AARSs have evolved to be more structurally complex through the addition of appended domains, without losing the ability to facilitate protein synthesis.
Consistent with this hypothesis, a rich and diverse set of expanded functions for AARSs have been found in higher eukaryotes, and in particular for human tRNA synthetases. This data, which is based both on the direct analysis of individual domains, as well as the discovery of mutations in genes for tRNA synthetases that are causally linked to disease, but do not affect aminoacylation or protein synthesis activity, suggests that these newly appended domains, or Physiocrines, are central to the newly acquired non-canonical functions of AARSs.
Additionally, there is now increasing recognition that specific tRNA synthetases such as histidyl-tRNA synthetase (HARS, HRS, or HisRS) can be released or secreted from living cells and can provide important locally acting signals with, inter alia, immunomodulatory, chemotactic, and angiogenic properties. Direct confirmation of the role of AARS as extracellular signaling molecules has been obtained through studies showing the secretion and extracellular release of specific tRNA synthetases, as well as the direct demonstration that the addition of fragments of the tRNA synthetases comprising the newly appended domains (Physiocrines), but not other fragments lacking these domains, are active in a range of extracellular signaling pathways. These Physiocrines, including those derived from HRS, represent a new and previously untapped opportunity to develop new first in class therapeutic proteins to treat human disease.
Recent studies have also established that some tRNA synthetases include novel regulatory genetic elements, including ALU elements (Rudinger-Thirion et al., PNAS USA. 108(40):E794-E802, 2011) that provide for increased cell type specific expression, or alternative splicing of specific tRNA synthetases in specific tissues, or in the context of specific diseases. Moreover some Physiocrines are proteolytically produced in response to particular stimuli in a cell type specific fashion. Consistent with the cell type specific over expression and extracellular release of Physiocrines, several autoimmune diseases, (generally referred to as ant-synthetase syndromes) are associated with the production of antibodies to a defined group of tRNA synthetases (Tzioufas Orphanet (2001) 1-5; Park et al., Rheumatol. Int. 31:529-532, 2011).
Autoimmune disorders arise when the immune system reacts against its own tissues. Autoimmune diseases are often classified on the basis of whether a single organ or tissue is involved or whether multiple organs or tissues are involved. Generalized or systemic autoimmune diseases, such as systemic lupus erythematosus (SLE), characterized by the involvement of multiple organs and tissues, are often associated with the presence of autoantibodies to fundamental cellular components. Other autoimmune diseases are characterized by autoantibodies to antigens associated with a single organ or tissue.
Systemic autoimmune diseases are typically characterized by the presence of autoantibodies. Some of the autoantibodies associated with the particular disease may be disease specific and others may be common to many autoimmune diseases. For example, SLE, which is a prototypical immune disorder, is characterized by the presence of autoantibodies that are detectable in other autoimmune disease, such as anti-single-strand DNA antibodies, anti-histones antibodies, and anti-ribonuclear particle (RNP) antibodies, and also by the presence of autoantibodies that are SLE-specific, such as the anti-double-stranded DNA antibodies. Other systemic autoimmune disorders, such as rheumatoid arthritis and (idiopathic) inflammatory myopathies, are also characterized by the presence of autoantibodies in the sera of patients that react with fundamental nuclear and cytoplasmic intracellular components. As with SLE, some of these autoantibodies are associated with other autoimmune disorders and some are specifically associated with autoimmune myositis.
The (idiopathic) inflammatory myopathies polymyositis, dermatomyositis and the related disorders, such as polymyositis-scleroderma overlap, are inflammatory myopathies that are characterized by chronic muscle inflammation and proximal muscle weakness. The muscle inflammation causes muscle tenderness, muscle weakness, and ultimately muscle atrophy and fibrosis as described by Plotz et al., Annals of Internal Med. 111:143-157, 1989; and Wallace et al., J. Musculoskelat Med. 27 (12) 470-479, 2010. Also associated with the muscle inflammation are elevated serum levels of aldolase, creatine kinase, transaminases (such as alanine aminotransferase and aspartate aminotransferase) and lactic dehydrogenase. Other systems besides muscle can be affected by these conditions, resulting in arthritis, Raynaud's phenomenon, and interstitial lung disease. Clinically, polymyositis and dermatomyositis are distinguished by the presence of a characteristic rash in patients with dermatomyositis. Differences in the myositis of these conditions can be distinguished in some studies of muscle pathology.
Interstitial lung disease (ILD) comprises a heterogeneous group of disorders in which fibrosis and inflammation occur within alveolar walls or in the loose tissue surrounding peribronchovascular sheaths, interlobular septa and the visceral pleura. Different forms of ILD are known which comprise, or are associated with, various autoimmune diseases in addition to myositis, including for example, hypersensitivity pneumonitis, scleroderma, systemic lupus erythematosus, rheumatoid arthritis, Churg-Strauss syndrome, Wegener's granulomatosis, and Good-pasture Syndrome.
Inflammatory muscle disease (IMD) and interstitial lung disease (ILD) are serious chronic potentially life threatening autoimmune diseases, for which the current standard of care includes non-specific anti-inflammatory drugs such as corticosteroids with the potential for important side effects. The cause of the on-set of these diseases has not yet been established, although autoantibodies can be detected in about 90% of patients with polymyositis and dermatomyositis according to Reichlin and Arnett, Arthritis and Rheum. 27:1150-1156, 1984. Sera from about 60% of these patients form precipitates with bovine thymus or human spleen extracts on Ouchterlony immunodiffusion (ID), while sera from about 80% of these patients stain tissue culture substrates, such as HEp-2 cells, by indirect immunofluorescence (IIF) (Targoff and Reichlin, Arthritis and Rheum. 28:796-803, 1985; Nishikai and Reichlin, Arthritis and Rheum. 23:881-888, 1980; and Reichlin et al., J. Clin. Immunol. 4:40-44, 1984). There are numerous precipitating autoantibody specificities in myositis patients, but each individual antibody specificity occurs in only a fraction of the patients.
Many autoantibodies associated with myositis or myositis-overlap syndrome have been defined and in some cases the antibodies have been identified (See U.S. Pat. No. 6,610,823, Antigens associated with polymyositis and with dermatomyositis). These include antibodies that are present in other disorders and also disease-specific antibodies as described by Targoff and Reichlin, Mt. Sinai J. of Med. 55:487-493, 1988.
For example, a group of myositis-associated autoantibodies have been identified which are directed at cytoplasmic proteins that are related to tRNA and protein synthesis, particularly aminoacyl-tRNA synthetases. These include anti-Jo-1, which is directed against histidyl-tRNA synthetase and is the most common autoantibody associated with myositis autoimmune disorders (about 20 to 40% of such patients according to Nishikai and Reichlin, Arthritis Rheum. 23:881-888, 1980); anti-PL-7, which is directed against threonyl-tRNA synthetase; anti-PL-12, which is directed against alanyl-tRNA synthetase, anti-OJ, which is directed against isoleucyl-tRNA synthetase, anti-EJ, which is directed against glycyl-tRNA synthetase, anti-KS which is directed against asparginyl-tRNA synthetase (see generally, Targoff, Curr. Opin. Rheumatol. 12 475-481, 2000) and against phenylalanine-tRNA synthetase (Betteridge et al., Rheumat. 46 1005-1008, 2007). A characteristic group of features is often associated with anti-synthetases (Love et al., Medicine. 70:360-374, 1991).
Anti-U1 RNP, which is frequently found in patients with SLE, may also be found in mixed connective tissue disease, overlap syndromes involving myositis, or in some cases of myositis alone. This antibody reacts with proteins that are uniquely present on the U1 small nuclear ribonucleoprotein, one of the nuclear RNPs that are involved in splicing mRNA. Autoantibodies that are associated with other conditions are sometimes found in patients with overlap syndrome such as anti-Sm, anti-Ro/SSA and anti-La/SSB. Anti-Ku has been found in myositis-scleroderma overlap syndrome and in SLE. The Ku antigen is a DNA binding protein complex with two polypeptide components, both of which have been cloned. Anti-Jo-1 and other anti-synthetases are disease-specific. Other myositis-associated antibodies are anti-PM-Scl, which is present in about 5-10% of myositis patients, many of whom have polymyositis-scleroderma overlap, and anti-Mi-2, which is present in about 8% of myositis patients, almost exclusively in dermatomyositis. Anti-Mi-2 is found in high titer in about 20% of all dermatomyositis patients and in low titer, by ELISA only, in less than 5% of polymyositis patients (Targoff and Reichlin, Mt. Sinai J. of Med. 55:487-493, 1988).
Typically patients with inflammatory muscle disease (IMD) and interstitial lung disease (ILD) present when relatively young and in otherwise in good health, unfortunately in a sub set of patients disease progression can result in significant disability and high morbidity. Moreover currently there are no drugs specifically approved for the treatment of the general population of IMD and ILD. The current standard of care, is to administer non-specific anti-inflammatory and immune modulatory drugs such as methotrexate or azathioprine, and if symptoms don't abate, cyclosporine (Wallace et al., J. Musculoskelat Med. 27:470-479, 2010). These drugs carry a substantive risk of side effects that can be severe with chronic administration. In severe progressive disease, individuals may be treated with intravenous immune globulin (IVIG). The burden and cost of care of treating patients with IVIG is high (as much as $10,000 per patient per monthly treatment), and a significant fraction of patients fail treatment and die.
Accordingly there remains a significant unmet need for improved methods of treatment of inflammatory muscle disease and related conditions that are both therapeutically and cost effective.